Leela, the young exotic dancer at the center of “Beautiful Thing,” is a genius of vulgarity. In this intimate and valuable book of literary reportage by Sonia Faleiro nearly every word out of Leela’s mouth is spit like a cartoon hornet. Few of these sentences, alas, are publishable here.

Nineteen when Ms. Faleiro met her, Leela was the highest paid bar dancer in a seedy Mumbai club called Night Lovers. She wore an “imported-padded” bra and had butterscotch streaks in her long hair; she sneered at most of the men who paid to watch her. When they’d toss small denomination rupee notes, she’d mock them: “Is this all you think I’m worth? Why shouldn’t I commit suicide? Why shouldn’t I stick my head into an oven?”

Leela’s way with a dirty phrase seems to infect Ms. Faleiro, a gifted young Indian-born writer who is previously the author of a novel called “The Girl” (2006). Her language, like dots of colored light pinging from a smudgy mirrored ball, casts an intoxicating if unsettling glow.

About one aggressive man at Night Lovers, the author observes: “Leela’s customer stank of vodka-chicken-onion-chili-lemon and clearly he was no hi-fi-super-badiya-tiptop type. He had no upbringing.” Plenty of Ms. Faleiro’s best sentences are unpublishable too.

“Beautiful Thing” is a book about Mumbai’s notorious sex industry, and the news it brings about young women’s lives will break your heart several times over. Most are from small villages. Most were raped repeatedly when young, often by relatives. Many were sold to other men.

Leela ran away to Mumbai when she was 13, after her father tried to film her nude and in suggestive poses, hoping she could be a porn actress. When she protested, he had her arrested, and she was raped by policemen. She fled from the general horror inflicted on India’s poor young women, in search of a better life.

Dancing at Night Lovers was, socially and financially, a step up for her. Bar dancers ranked above other sex workers, Ms. Faleiro explains, “because selling sex wasn’t a bar dancer’s primary occupation and because when she did sell sex she did so quietly and most often under her own covers.”

What Leela wants, Leela rarely gets. She dreams of a Bollywood career, and of a good marriage. She’s forced instead to live by her taut body and her even-more-taut wits. “She squeezed the men in her life like they were lemons,” Ms. Faleiro writes, “and once she was through, she discarded them like rinds.”

Leela is aware of the limited but genuine power she wields. “They think I dance for them,” she declares of her customers. “But really, they dance for me.”

Ms. Faleiro’s book has a resonance that belies its compact size. She focuses on only a few characters: Leela, some of her dancer friends and Shetty, the wily owner of Night Lovers. If “Beautiful Thing” were to be made into a film, Shetty would be played by whomever is the current Bollywood equivalent of Paul Giamatti.

With a few strokes Ms. Faleiro conjures a world, and it is mostly a world of hurt and confusion. She spent five years researching and writing this book, and its lessons are presented frankly. “Poverty eventually made criminals of everyone,” she writes of the women and the shady men in their milieu. Noting Mumbai’s unforgiving nature, she says, “Naïveté was fair prey and beauty unguarded deserved what it got.”

In another writer’s hands Leela’s story might have become an op-ed tract. But Ms. Faleiro’s book is not a dirge. For one thing Leela is simply too quirky and alive on the page. She might be wealthy from the tips she makes, but the author catches her in unguarded moments.

“She loved not paying for her pleasures,” Ms. Faleiro writes. “After the dance bar closed for the night, Leela would waltz from table to table helping herself to half-smoked cigarettes. She would press her cherry-red lips to abandoned beer bottles.”

There’s a feminist spark in Ms. Faleiro’s portrayal of these women. One who was raped repeatedly before the age of 10 says to her, “I decided that if this was going to keep happening to me, then at least I should profit from it, I should eat from it.”

Leela urges the author not to pity her. “When you look at my life, don’t look at it beside yours,” she implores. “Look at it beside the life of my mother and her mother and my sisters-in-law who have to take permission to walk down the road.”

This story can’t end well, and of course it does not. The dance club closes; Leela vanishes into prostitution while the author searches for her. Ultimately Leela loses a tooth in a beating, and she and a friend leave to work in Dubai at the urging of a gangster. You hate to think where she is at this moment.

This book, by its end, seems to have taken something out of Ms. Faleiro. You get the sense she’d like to close with even a hint of optimism, but that’s hard to muster. Instead she quotes the gangster, Sharma, who explains that Leela will probably someday preside over a small brothel herself.

Sharma issues a line that will ring in your ears. “She will sell her daughter, even if she is her only child, her only family, because her mother sold her, and who is her daughter to deserve better?”

Leela, were she to read “Beautiful Thing,” would probably spark up a cigarette and tell us where to stuff our horror and pity. She’d agree with the dancers who declared, within the author’s earshot, “Tears are the indulgences of those who haven’t suffered enough.”